Usually, when factories purchase injection molding machines, they choose the injection molding machine with the appropriate injection volume according to the weight of their products. But many people don't quite understand the theoretical injection volume, theoretical injection volume, and actual injection volume provided by some injection molding machine manufacturers. Now, the calculation method of these data and the common sense of how to choose an injection molding machine according to plastic parts.
The introduction is as follows:
1. Theoretical injection volume and theoretical injection volume
The theoretical injection volume is calculated according to the design value, the formula is V= π/4 Ds2*S (formula 1) V-on the injection volume cm3Ds-screw diameter cmS-injection stroke cm
The theoretical injection volume is equal to the theoretical injection volume multiplied by the density of the plastic at normal temperature:
G=VXρ (Formula 2)
G-theoretical injection volume g
V-theoretical injection volume cm3
ρ-plastic density at room temperature g/cm3
Based on the characteristics of polystyrene (ps) plastic, its density value is usually used as the calculation standard: the density of ps at room temperature is 1.05g/cm3. For example, the 160F machine in the company's product version has a theoretical injection volume of 307cm3, and the theoretical injection volume is 307×1.05=322.4g
2. The actual injection volume and injection volume
The volume required for each injection is obtained by multiplying the weight of each cavity material by the number of cavities, plus the weight of the gate and flow, and then divided by the density of the plastic at the mold temperature: V= G/ρdeposit Xη (Formula 3) V-theoretical injection deposit cm3G-actual maximum injection volume gρ-density of plastic at molding temperature g/cm3η-efficiency safety factor of bolting apron
Considering that the plastic melt flows back before the rubber ring is closed and with the gap between the rubber ring and the barrel during the injection process, a safety factor η is included. For most plastics, η is 0.97, for nylon η is 0.95.
At present, the injection volume and injection volume marked in the company's injection molding machine F3, F3J, PVC, PET and other series of product catalogs are obtained according to the above formula and polystyrene density standards. For example: 160F2 machine, injection volume V=329cm3, dense pair ρ melt=0.93g/cm3, ξ=0.97 at the melting temperature of ps, calculated by formula (3), the actual maximum injection volume is 296g.
For polystyrene (PS), another empirical calculation method for the actual injection volume is to multiply the theoretical injection volume by a coefficient and multiply it by the density of polystyrene at room temperature:
G=V×ρ×α
G - the maximum actual injection volume g
V-theoretical injection volume cm3
The density of ρ-ps at room temperature is 1.05g/cm3
α-coefficient
According to the national industry standard JB/T7267.94, the value of α is 0.85
